This invention relates to the use of high flash point, low vapor pressure compositions for injection into, and coating of, gas and oil wells and surrounding underground formations and processing equipment for the purpose of removing scale, paraffins, tars, and other viscous constituents. Treatment results in increased flow of gas and/or oil and decreased adhesion of soils and scale in all aspects of oil and gas recovery, including formations, casing perforations, casings, lines, tanks, and pumping equipment.
The efficient recovery of oil and gas from wells depends on maintaining clean formations, casing perforations, lines and pumping equipment. Oil wells have a problem with the build up of paraffin, sulfur, scale, heavy oil, and tar by-products. These residues foul the wells and the casing perforations and the lines that carry the oil or gas to the surface, and foul the pumps and metal rods which are used to recover the oil or gas from the well.
Typical prior art methods consist of four major types of products. The first method uses aggressive blends of aromatic and/or aliphatic petroleum hydrocarbons or halogenated hydrocarbons. These products may or may not contain surfactants to allow the products to mix with and emulsify in water to increase cleaning efficiency. The presence of water decreases the efficiency of these compositions significantly. Pure solvent blends are immiscible in water and cannot penetrate to the soils. The addition of emulsifiers allows the solvents to blend with the water, but the resulting solvent/emulsion system is not as efficient a cleaner as the pure solvent.
The second method is the use of bacteria to digest the paraffinic and tar-based soils. This system is very dependent on well temperature and is sensitive to environmental factors such as the composition of the oil. This process is typically slower than the solvent-based process.
The third method is predicated on water-based alkaline, hard-surface cleaners. These cleaners generally incorporate alkaline builders, water-soluble solvents, such as glycol ethers, alcohols, and surfactants. Alkaline builders consist of hydroxide, carbonate, phosphate, and silicate. Water-soluble solvents typically consist of ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol ethers. Typical surfactants are the categories of alkyl phenol ethoxylates, linear alcohol ethoxylates, or alkyl sulfonates, amphoterics, and fatty acid soaps of alkanolamides. The cleaning efficiency of these alkaline compositions on paraffins and other oil-based soils is typically much lower than that of solvent blends. Further, these compositions are not effective for removing scale.
The fourth method of cleaning involves the use of hot oil, which is injected into the well. The hot oil melts and dissolves the paraffins and other oil byproducts and carries them to the surface. Although this method is efficient, the use of hot oil creates a hazardous condition and can adversely affect the wells.
Typical prior art compositions employ solvents of aromatic and/or aliphatic petroleum hydrocarbons or halogenated hydrocarbons. These solvents produce vapor emissions, commonly known as xe2x80x9cVOCsxe2x80x9d (volatile organic compounds), which typically are toxic. Other cleaning compositions require little or no VOCs, but require high levels of caustic and/or phosphates which cause problems in transportation, use, and disposal.
There are many problems associated with the above-mentioned methods and solvents. For example, halogenated hydrocarbons affect worker health adversely and are ozone-depleting chemicals. Some of the solvents and methods may adversely affect the quality of the oil or gas. Many of the non-halogenated solvents used are either flammable or combustible, resulting in increased fire and explosion risks and higher insurance premiums. Furthermore, the disposal of the spent solvents, in accordance with government regulations, is expensive. In fact, most of the halogenated solvents are subject to high taxes and are in the process of being phased out. In addition to the above-mentioned problems, limits on the amount of VOCs that may be emitted into the atmosphere are set by the Environmental protection Agency, as specified by the xe2x80x9cClean Air Act.xe2x80x9d These limits are determined by the solvent content of the incoming production of raw material versus the solvent content of the waste or finished products.
The bacteria-based cleaning solution also has other disadvantages. The treatment requires that the well be shut down for two weeks to allow the establishment of a bacterial colony. When pumping is resumed, the bacteria are removed with the oil, which results in rapid depletion of the colony and retreatment is required.
An object of the present invention is to provide a method of cleaning gas and oil wells, equipment, well casing perforations, and surrounding formations, pumps, as well as lines, pipes, and the like using an effective cleaning composition which is free of objectionable petroleum-derived or halogenated hydrocarbon and alkaline solvents and useful in removing most of the soils and scale encountered in gas- and oil-well cleaning operations.
Another object is to use a composition which is safe and biodegradable.
A further object is to use a composition capable of functioning at ambient temperatures and at elevated temperatures.
A further object is to use a safe liquid cleaning composition containing fatty acid methyl esters and lower alkyl glycol ethers, which is effective in removing paraffins, tars, related soils, and scale from gas- and oil-wells, casings and equipment.
An additional object is to use a low VOC composition ( less than 50%), which is effective as a cleaner for gas- and oil-wells, casings and equipment.
An additional object of the invention is to use a composition with a flash point above 200xc2x0 F.
A further object is to use a composition which will produce a coating on well casings, lines, pumps, pipes and other equipment, to prevent the adhesion and accumulation of paraffins, other related soils, and scale on these parts, to help retard corrosion, and to allow more efficient operation and consistent production between cleanings.
An additional object is to provide a composition which is low evaporative, widely dispersive, and results in differential wetting of well structures and equipment.
An additional object is to provide enhanced gas and oil recovery from wells.
A further object is a method to separate excess water from recovered crude petroleum oil.
The present invention is directed to a method for removing and preventing the buildup of soils, scale, or both, from gas or oil wells, hydrocarbon bearing formations, and recovery, pumping, storage, and transmission equipment, comprising introducing into said well, formation or equipment a composition comprising about 40 to 99 wt % of a fatty acid alkyl ester blend and about 1 to 25 wt % of at least one lower alkyl glycol ether.
The present invention is also directed to a method for separating excess water, sludge, or both, from recovered crude petroleum oil comprising adding to the crude petroleum oil a composition comprising about 40 to 99 wt % of a fatty acid alkyl ester blend and about 1 to 25 wt % of at least one lower alkyl glycol ether, and then agitating the mixture.
In addition, the present invention provides an improved fracing process of forcing sand and/or another granular material into an oil or gas formation under pressure, whereby the improvement comprises mixing the sand with a composition comprising about 40 to 99 wt % of a fatty acid allyl ester blend and about 1 to 25 wt % of at least one lower alkyl glycol ether.
The most common industrial uses of fatty acid alkyl ester blends are as industrial metal working lubricants, in soap manufacturing, as a plasticizer for waxes and as solvents in the formulation of industrial oils and leather treating compounds. These compounds are also used as textile lubricants and foam depressants, and also in the formulation of low VOC press washes.
It was discovered that combining fatty acid alkyl ester blends with lower alkyl glycol ethers provides cleaning compositions having excellent properties, i.e., high flash point, good soil and paraffin penetration, and excellent protection against resoiling and scale buildup. The compositions used in the methods of the present invention are blended to provide low VOCs (less than 50%) and to provide a composition with a flash point above 200xc2x0 F. TCC (tag closed cup). The compositions are also safe and biodegradable.
The present invention is directed to methods for removing and preventing the buildup of paraffins, other related soils, and scale from gas and oil wells, hydrocarbon bearing formations, and recovery, pumping, storage, and transmission equipment by injecting into the wells and such equipment a cleaning composition comprising about 40 to 99% by weight of a fatty acid alkyl ester blend; and about 1 to 25% by weight of at least one lower alkyl glycol ether, with the remainder being suitable additives. Preferably the composition contains about 60 to 95% by weight, more preferably about 80 to 90% by weight, of the fatty acid alkyl ester blend, and preferably about 1 to 15% by weight of the lower alkyl glycol ether.
There are many types of soils which buildup in gas and oil wells and processing equipment, such as paraffins, tar by-products, and other viscous soils. Further, the buildup of scale is a problem in such wells and equipment. Scale is typically, but not limited to, the accumulation of calcium carbonate deposits and/or iron oxide and other hard residual deposits. The composition of the present invention is effective to remove many types of soils and scale associated with gas and oil recovery and processing and thus enhance the oil recovery process.
The gas and oil processing equipment includes all types and varieties of equipment associated with gas and oil recovery and processing, for example, gas and oil well casings, pumps, pipes, lines, tanks, and the like. It is contemplated that the present composition may be used with all such equipment.
There are several ways that the method of removing or preventing soils and/or scale buildup in gas and oil wells and equipment may be implemented using a composition in accordance with the present invention.
In addition to cleaning the wells and associated equipment, it is often desirable to introduce the composition, through the perforations in the casing, into the surrounding formation. The composition may be forced into the surrounding formation by applied pressure or, if the composition is allowed to set at the bottom of the casing, the composition may seep into the formation without additional pressure. The composition permeates the formation, dissolving blockages in the formation to provide more efficient oil and gas recovery.
A method of cleaning and maintaining a working well, including the surrounding formation, includes the steps of pouring or injecting the composition down the casing side (back lines) of a well and allowing it to mix with the fluid which is already in the well. When enough fluid is present, the composition is then circulated by a pump for 24-72 hours, preferably 48-72 hours. Prior to circulating, the composition may be allowed to set for 8 to 24 hours, for example. The setting time, circulating time and dosage depend on the amount of soil and/or scale anticipated to be present as well as the depth of the well. A basic initial dosage can be, but is not limited to, 20 gallons of composition and for maintaining a clear structure, at least about 5 gallons of composition per well on a periodic basis, e.g. biweekly, monthly, bimonthly.
If there is a great amount of soil and/or scale present in the well or associated equipment, if the pump or rods are frozen, or if the surrounding formation is clogged, alternative methods may be necessary. Thus another method of cleaning and maintaining a working well, including the surrounding formation, initially mixes oil and the composition at ambient temperatures and then introduces the mixture into the casing. The ratio of oil and composition and the amount of the mixture introduced depends on the amount and type of soil and scale present in the well and on associated equipment. The mixture can contain about 10-200 gallons of composition for every 40 barrels of oil. Preferably the mixture contains about 20 gallons of composition for every 40 barrels of oil. The mixture is pumped down the backside or casing side of the well. The mixture is usually allowed to set prior to circulating. The mixture may be used at ambient temperature or may be heated to 150-160xc2x0 F. prior to introduction to the well.
In another embodiment, the composition and oil may be introduced into the well separately, at ambient or elevated temperatures, preferably with the composition being introduced first and forced into the formation by the weight of the oil. The mixture may then be allowed to set, circulated, or both.
In other embodiments water is substituted for the oil. As with the oil, the water and composition may be mixed prior to introduction to the well or introduced separately. The water temperature may be ambient temperature or elevated to about 150-160xc2x0 F. Again, the mixture may be allowed to set, circulated, or both.
After introducing into a well, the composition of the present invention coats the surfaces of the well, formations, and associated equipment to clean and to prevent the future adhesion and accumulation of paraffins, other soils, and scale. The composition may also be applied directly to the equipment. For example, prior to placing rods and casings into gas and/or oil wells, these parts may be sprayed with the composition, or the parts may be dipped into tanks filled with the composition to prevent corrosion and buildup of scale and soils.
The composition may be introduced by means of injection pumps into off-shore gas or oil wells to reduce soils, particularly paraffin, or scale adhesion in well casings and transmission lines. In addition to the problems associated with land oil wells, off shore wells have the further problem of the ocean or sea water behaving as a coolant of the lines and contents between the bottom of the ocean and the platform. Thus off shore wells have a particular problem with paraffin buildup. To treat the lines, 40-50 gallons of the composition, for example, are dropped into the lines. Preferably, the composition is heated prior to being introduced into the lines.
The composition used in the methods of the claimed invention contains ingredients in amounts effective to clean the wells, formations, and equipment and/or to provide an effective coating on their surfaces to prevent future buildup of soils and scale and corrosion. The composition is low evaporative and provides differential wetting of the surfaces; thus, the composition will not evaporate to any significant extent and it will provide a coating that remains on the surface for useful periods of time.
The fatty acid alkyl ester blends useful in compositions of the present invention preferably contain C2 to C8 esters of C4 to C22 fatty acids having the formula: 
wherein R1 is C4 to C22 alkyl and R2 is C1 to C8 alkyl. Fatty acid esters are derived from natural products, and thus comprise more than one ester; hence blend. Typically, fatty acid esters are derived from the esterification of fatty acids or the transesterification of animal fats or vegetable oils.
The fatty acid alkyl ester blend more preferably contains methyl, ethyl, n-propyl, isopropyl, or n-butyl esters of C4 to C22 fatty acids. Most preferably, the fatty acid alkyl ester blend contains methyl esters. The fatty acid methyl ester blends are preferably blends with a cloud point of 40xc2x0 F. and a high degree of unsaturation to increase solvency. More preferably, the fatty acid methyl ester blends are derived from soya, canola, and other vegetable oils, with a cloud point of 20xc2x0-32xc2x0 F. and an iodine value of 90-130.
1 to 25 wt. % of a lower alkyl glycol ether may be added as a penetrant, to reduce viscosity of the mixture, as a coupling agent, and/or to increase efficacy on hydrophilic soils. Examples of lower alkyl glycol ethers useful in the present composition include dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, ethylene and diethylene glycol ether, methyl, ethyl, propyl and butyl ethers, such as ethylene glycol monobutyl ether, or mixtures thereof.
A polyoxyalkylene glycol ether may be present in the composition in amounts of about 1 to 40 wt. %, preferably 3 to 25 wt. %, and most preferably 3 to 10 wt. %. The actual amount utilized depends on the types of soil present in the equipment to be cleaned and on the water content of the well or equipment being cleaned. Preferably used are polyethylene glycol ethers and polypropylene glycol ethers having the formulas:
Rxe2x80x94Oxe2x80x94(C2H4O)xH and Rxe2x80x94Oxe2x80x94(C3H6O)xH
where, in each formula, R is C1 to C8 alkyl and x is greater than 4. R is preferably methyl, ethyl, propyl, or butyl. More preferably, the polyoxyalkylene glycol ether is an n-butoxy polyalkylene glycol ether. Commercial polyoxyalkylene glycol ether formulations available include Macol 300, Macol 660, WSL-2000, WSL-3520, and WSL-5100 produced by PPG Mazer, Gurnee, Ill. The polyoxyalkylene glycol ether preferably has a molecular weight of between about 200 and 600 and a viscosity of between about 15 and 150 cps when measured at 25xc2x0 C. using a Brookfield LVT Viscometer with a No.2 spindle at 60 r.p.m.
Preferably, at least 1 wt %, more preferably, 1.5 to 3 wt %, of antioxidants are included in the composition. Antioxidants suitable for the present invention include, but are not limited to, (BHT) 2,6-di-tert-butyl-para-cresol, (BHA) 2,6-di-tert-butyl-para-anisole, Eastman inhibitor O A B M-oxalyl bis(benzylidenehydrazide), and Eastman DTBMA 2,5-di-tert-butylhydroquinone. A surfactant may also be added to the composition. Any surfactant suitable for use in cleaning oily soils may be used, such as ethoxylated nonylphenols, linear alcohol ethoxylates, alkanolamine salts of dodecylbenzene sulfonic acid, sulfosuccinates, phosphate esters, alcohol sulfates, quaternary ammonium compounds, amphoteric surfactants, alpha-olefin sulfonates, sorbitan, and fatty acid derivatives. The surfactant is added in an amount effective to perform as a wetting agent and emulsifier, and usually up to 10 wt. %, preferably 1-3 wt %, of the composition.
Commercial surfactants include the EXXATE series of surfactants obtained from EXXON. EXXATE 1000 is an acetic acid ester of C9-C11 branched oxo-alcohol. DBE (DuPont) is a blend of 45-75 wt. % dimethyl glutarate, 10-25 wt. % dimethyl adipate, and 15-30 wt. % dimethyl succinate.
Up to 50 wt. % of other additives may be added, as needed, for particular applications, such as to vary the VOC levels, increase penetration of the mixture, decrease viscosity of the mixture, as couplers for solvents insoluble in the mixture, and to provide solvents for oleophilic and hydrophilic soils. It is within the skill of the art to determine the amount and type of additive needed for a particular application.
Suitable additives include terpenes, terpene alcohols, C8-C14 alcohol ester blends, glycols, acid esters, diacid esters, petroleum hydrocarbons, amino acids, alkanolamines, and amines. Examples of terpenes include d-limonene and xcex1 and xcex2 pinene and terpene alcohols, including a-terpineol. C8-C14 alcohol ester blends include EXXATE 900, 1000, and 1300 from Exxon Chemical; glycols include propylene glycol, dipropylene glycol, and tripropylene glycol. Acid esters include methyl oleate and methyl linoleate, and diacid esters include methyl or butyl diesters of glutaric, adipic, and succinic acids. Petroleum hydrocarbons include AROMATIC 100, AROMATIC 150, ISOPAR M, and ISOPAR K.
Amines such as morpholene, 1,3-dimethyl-2-imidazolidinone, 1,3 propanediamine, 2-amino-1,3-propanediol, and 3-amino propanol, and alkanolamines such as triethanolamine, diethanolamine, 2-aminomethyl propanol, and monoethanolamine act as dispersants for soils and solubilize fatty acids and oils. Amino acids, such as choline and choline hydroxide, provide nontoxic alternatives to monoethanolamine, and act as metal chelators, preferably, methyl or isobutylesters of C4-C6 aliphatic dibasic esters and n-methyl-2 pyrrolidone. Preferably up to 5 wt % of n-methyl-2 pyrrolidone is included.
Other additives typically used in cleaning compositions may be used, including water softening agents, sequesterants, and corrosion inhibitors, which are added in amounts effective to perform their intended function. These additives and amounts thereof are well within the skill of the art. Suitable water softening agents include linear phosphates, styrene-maleic acid co-polymers, and polyacrylates. Suitable sequesterants include 1,3-dimethyl-2-imidazolidinone, 1-phenyl-3-isoheptyl-1,3-propanedione, and 2-hydroxy-5-nonylacetophenoneoxime. Examples of corrosion inhibitors include 2-aminomethyl propanol, diethylethanolamine benzotriazole, and methyl benzotriazole.
All additives preferably have a flash point greater than 190xc2x0 F. TCC in order to achieve a final composition flash point greater than 200xc2x0 F.
Typical treatment of a well requires pumping the cleaning solution into the well casing, and circulating the solution from 24 to 72 hours. A typical well has a 4xc2xdxe2x80x3 casing which extends down through the depth of the well. The 4xc2xdxe2x80x3 casing at the surface is capped by a well head. The well head has a fitting on top through which 2xe2x85x9cxe2x80x3 tubing is inserted. The tubing can extend to the bottom of the well and can be removed in sections for cleaning and maintenance. There are two 2-inch ports on the side of the well head which support the back lines. The normal procedure consists of injecting 5 to 20 gallons of the cleaning solution into the casing side of the well (back lines), and circulating it up the central 2xe2x85x9cxe2x80x3 tubing. The depth of the well, casing diameter, and anticipated amount and nature of the soils, determine the exact dosage needed. The flow of the cleaning solution is maintained for 24 to 72 hours to remove all soils. Depending on buildup, repeated treatments may be provided every 2 to 3 weeks.
Another embodiment of the present invention is directed to a method for separating excess water and sludge from recovered crude petroleum oil. Crude oil contaminated with sludge and/or water is not pure enough for resale. The water or sludge is generally removed by xe2x80x9crollingxe2x80x9d the tank via injecting natural gas under pressure or by adding dry ice to cause agitation of the liquid. The process of oil/water or oil/sludge separation is slow unless an accelerator is added. Thus a further embodiment of the present invention comprises adding to the crude petroleum oil in an amount to accelerate oil/water or oil/sludge separation, a composition comprising about 40 to 99 wt. % of a fatty acid alkyl ester blend and about 1 to 25 wt. % of at least one lower alkyl glycol ether and then agitating to mix.
Typically 1-100 gallons of composition are used to separate water and sludge from 100-400 barrels of oil. The composition is added to the tank and then the tank is xe2x80x9crolledxe2x80x9d by introducing natural gas or carbon dioxide for about 24 hours. The use of the composition in the tank resulted in complete separation of the water, which was removed from the bottom of the holding tank. Standard indicator test strips or indicator reagents for water in oil indicated no detectable level of water.
Further, the composition may be added to crude oil, in amounts of 0.001 to 0.01% by weight, to reduce the formation of sludge and paraffins in oil transported through transmission pipelines, including offshore pipelines.
Other applications using the composition of the present invention include adding the composition during fracing processes, that is the during the process of forcing sand or other material into a hydrocarbon bearing formation under pressure. In accordance with the present invention, the composition is mixed with the sand or other material at a rate of, for example, 1-5 gallons per cubic yard. The sand/composition blend is forced into the a hydrocarbon bearing formation by any one of a variety of methods. Such methods include, but are not limited to, carbon dioxide injection, oil injection, gel injection, and sand/slurry injection.